This invention relates to a steering geometry and machine configuration for a vehicle. It is particularly concerned with unmanned, automated vehicles used for floor maintenance such as sweepers, scrubbers, vacuum cleaners and the like, although it is also applicable to machines that carry an operator.
Many conventional manned floor maintenance machines typically have three wheels; two idlers in front and a steerable driving wheel in the rear. The nature of a floor machine's work routinely requires that it operate along a wall and as close as possible to it. A variation on this is operating as close as possible to boxes, furniture, or other items beside the path of the machine. This presents much the same problem as operating along a wall, so only a wall will be referred to. At some point it usually becomes necessary to turn the machine away from the wall. However, with a conventional, rear steered vehicle this maneuver causes the rear end of the machine to swing toward the wall, or into it if the driver is careless. For such a machine to turn away from a wall there has to be significant space between the machine and the wall before the turn is made. Such a machine cannot get away from a wall at all if there is no significant space there.
The approved technique for handling this maneuver on a rear steered manned vehicle is to slow down and steer a little bit away from the wall, swinging the rear corner of the machine almost into contact with the wall. The operator must then drive forward carefully, and gradually turn the steering wheel to hold the rear corner of the machine almost on the wall. The machine must travel along the wall for a number of feet while it slowly moves out on a tightening spiral course and finally has enough room to complete a normal radius turn. The maneuver requires considerable travel distance along the wall. It also requires a progressive steering response by the operator and careful manipulation to avoid scraping the wall or knocking over anything that may be stacked along an aisle.
The progressive response of a human operator produces a turn that has a constantly changing pivot point and radius. Incorporating this progressive response into the steering system of an unmanned vehicle is a formidable technical problem. It would require constant measurement of the separation between the wall and the closest part of the machine to the wall, with a variable steering control to hold that separation constant. Such constant measurement becomes virtually impossible when the machine is not operating along a continuous wall, but rather along the edge of an aisle bordered by intermittent vertical objects such as stacked boxes of various heights, or furniture. Therefore, duplication of human steering in an unmanned vehicle is a complex design problem. The present invention avoids the problem by configuring a vehicle in a manner which makes it much more maneuverable than conventional machines. It can be easily turned away from a wall at any reasonable speed, which eliminates the need for steering controls that measure clearances and progressively turn the vehicle. If desired, the vehicle may be turned about a fixed pivot point at a constant rate of turn, which further simplifies the control problem. The result is a more maneuverable, simpler, more economical machine which is more easily adapted to automated steering control. The invention can also provide a person-carrying vehicle which can be steered away from a wall by its operator more easily than can current rear steered vehicles.
Floor maintenance machines have also encountered a problem in trying to completely clean a floor in a corner of a room. The steering limitations of conventional machines as discussed above prevent them from driving completely into an inside corner, then turning immediately and following the second wall. A turn away from the first wall must be started some distance from the corner in order to be completed by the time the second wall is reached. A large area of floor in the corner will be untouched by the machine and must be cleaned by hand. The machine configuration of the present invention solves this problem. It allows the floor maintenance machine to drive along a wall all the way into an inside corner, then turn and follow the second wall. It will thus clean most of the floor area in a corner that a conventional machine leaves untouched.